[log in to unmask] wrote:
> 1.  I now have collections of messages sitting in Thunderbird on three
> different machines, with an extensive structure of folders 85-95%
> duplicated across all three.  How can I move the two smaller collections
> and merge them into the larger "main" one?

Make sure Thunderbird is not running.
On the "second" machine, find out where the mail folders are (it should 
be in your settings), go into that folder and start with something easy. 
Let's say you have a Personal folder and/or Personal mailbox files. 
Copy them, with a different name (my_personal), with subfolders(!) into 
the folder on the main machine where the inbox files live.

Start main Thunderbird, and you'll see the new my_personal folder. 
You'll be able to easily drag and drop what you want from there into the 
new Thunderbirds folders.

Once you have the hang of it, you can do the rest the same way.  I don't 
know if  you can do it at the main level in the old machine.  In other 
words, I don't know if you rename inbox files to my_inbox files, all 
folders, and then copy the entire mess at one fell swoop.

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